This project seeks to understand the common deficits of attention that result from unilateral brain damage caused by strokes or other injuries. Deficits of attention can lead to grave consequences during rehabilitation, and predispose patients to falls, with attendant complications and mortality. Despite the seriousness of deficits such as extinction and neglect, and the fact that they have been described for more than a century, they are poorly understood. Extinction refers to an inability to attend to, or perceive, stimuli on the side of space opposite to the site of a lesion (i.e., contralesional stimuli) when a stimulus is present in the unaffected side of space, ipsilateral to the lesion. Extinction can occur in vision, audition, tactile sense, and even gustation, but it is not known whether similar causes underlie it in different modalities. A major problem in understanding extinction is that subtle changes in the method of testing may lead to major differences in the clinical impression of a given patient. Specifically, this project will test a new theory of how brain damage may lead to the phenomenon of extinction, although the results of this study will generalize to other deficits of attention. The present theory proposes that extinction in vision, audition and taction following cortical lesions, arises when the identity and location of stimuli cannot be bound together. This proposal will be tested using behavioral tasks that require patients to bind both these aspects of stimuli together, and tasks that do not. It is predicted that tasks that require binding will lead to much higher error rates than tasks that do not. It is suggested that a major source of inconsistency in clinical testing is that some tests make lower demands on binding than others, leading to great differences in the detected levels of inattention. A novel aspect of the present study is that visual, auditory and tactile extinction will all be tested using analogous tasks so that the general principles of our theory can be tested? Inherent in this view of extinction is the proposal that attentional failure arises independently within each perceptual modality, that, for example, visual extinction occurs as a binding failure of visual information. This contrasts with a view that overall unilateral inattention will lead to extinction in all modalities, and predicts that most patients will have extinction in only one or two modalities. The occasional co-existence of, say, visual and auditory extinction will be expected simply because areas crucial for auditory binding may be physically close to those crucial for visual binding, thus be affected by a single large lesion.